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Today the new Worldwide Harmonised Light Vehicle Test Procedure (WLTP) will be made mandatory.

It is a new standard measurement which carmakers will have to meet and follows the introduction of the Real Driving Emissions (RDE) introduced and used by some carmakers in Britain.

RDE puts cars through tougher emissions tests on the road instead of just in the laboratory like the older standards.

WLTP and RDE tests are significantly more comprehensive than the New European Driving Cycle (NEDC).

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(Image: WLTP)

It was first introduced in September 2017 but will become mandatory from September 1st, 2018 for all new cars.

Under the new tests, every car will be subject to a longer cycle of more varied driving.

Cars now undergo 23.5km of tests over 30 minute periods opposed to 11km of testing over a 20-minute test.

The average speed of the cars when tested also increase from 20 mph to 28 mph and a higher top speed of 80 mph compared to 70 mph.

There is also a longer period of extra-urban simulated driving each car will have to undergo.

As a result, previously recorded figures MPG and CO2 for a car should differ under the new testing.

It is estimated that CO2 emissions should increase by nine per cent on average across the board.

One example of how a car's MPG and CO2 emissions can change, reported on by CarKeys, revealed that under NEDC a Vauxhall Astra 1.6 CDTi EcoFlex diesel had fuel economy figures ranging from 67.3 to 85.6mpg.

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However, under WLTP the same car achieves figures ranging from 44.2 to 65.7mpg, a significant reduction.

Drivers should be aware that MPG figures whether provided by NEDC or WLTP are a guideline and are subject to change and have never been artificially represented by a carmaker.

Cars compliant with Euro 5 emissions will no longer be allowed to be sold as new cars from tomorrow.

The latest laboratory tests (WLTP) replace the old system (NEDC) and are designed to produce figures that are closer to what people will actually achieve in everyday use.